Ontogeny in the steinmanellines (Bivalvia: Trigoniida): an intra- and interspecific appraisal using the Early Cretaceous faunas from the Neuquén Basin as a case study

Despite the paleontological relevance and paleobiological interest of trigoniid bivalves, our knowledge of their ontogeny –an aspect of crucial evolutionary importance– remains limited. Here, we assess the intra- and interspecific ontogenetic variations exhibited by the genus Steinmanella Crickmay (Myophorellidae: Steinmanellinae) during the early Valanginian – late Hauterivian of Argentina, and explore some of their implications. The (ontogenetic) allometric trajectories of seven species recognized for this interval were estimated from longitudinal data using 3D geometric morphometrics, segmented regressions and model selection tools, and then compared using trajectory analysis and allometric spaces. Our results show that within-species shell shape variation describes biphasic ontogenetic trajectories, decoupled from ontogenetic changes shown by sculpture, and with a gradual decay in magnitude as ontogeny progresses. The mode of change characterizing each phase (crescentic growth and a...尽管三角蛤类双壳纲（trigoniid bivalves）具有重要的古生物学研究价值与古生物学生物学研究意义，但学界对其个体发育（ontogeny）——这一具有关键进化重要性的研究维度——的认知仍较为有限。本研究聚焦阿根廷凡兰吟阶早期至豪特里维阶晚期的斯坦曼蛤属（Steinmanella Crickmay，隶属肌壳蛤科斯坦曼蛤亚科Myophorellidae: Steinmanellinae），评估其展现出的种内与种间个体发育变异，并探讨相关研究启示。研究依托纵向数据，通过三维几何形态测量学（3D geometric morphometrics）、分段回归（segmented regressions）与模型选择工具（model selection tools），估算了该地质时段已识别的7个物种的异速生长轨迹（allometric trajectories），随后借助轨迹分析与异速生长空间（allometric spaces）对上述轨迹开展比较分析。研究结果表明，物种种内的壳体形状变异呈现双相个体发育轨迹，该轨迹与壳面纹饰（sculpture）的个体发育变化相互解耦，且随个体发育进程推进，变异幅度逐渐衰减。表征各发育阶段的变化模式（新月形生长阶段及……